Current reference sources are basic building blocks in analog circuit design. In some very low power applications, a reference current source is needed that will supply not more than, e.g., 20 nA. With a conventional approach, resistors of a very high value (in the order of several MΩ) are required for this purpose. Resistors of high value need a large area on the chip. While current sources can also be designed without resistors, they all show a positive temperature coefficient and are not suitable for applications that require a negative temperature coefficient, such as needed, e.g., for some type of oscillators.